Wartsila ?31DF Series Product Manual page 161

Wärtsilä 31DF Product Guide
11.2.10 Exhaust gas silencers
The exhaust gas silencing can be accomplished either by the patented Compact Silencer
System (CSS) technology or by the conventional exhaust gas silencer.
11.2.10.1 Exhaust noise
The unattenuated exhaust noise is typically measured in the exhaust duct. The in-duct
measurement is transformed into free field sound power through a number of correction
factors.
The spectrum of the required attenuation in the exhaust system is achieved when the free
field sound power (A) is transferred into sound pressure (B) at a certain point and compared
with the allowable sound pressure level (C).
Fig 11-7
The conventional silencer is able to reduce the sound level in a certain area of the frequency
spectrum. CSS is designed to cover the whole frequency spectrum.
DBAE248994
Exhaust noise, source power corrections
11. Exhaust Gas System
11-7